This kind of vehicle door frame includes a post and a substantially arcuate upper rim. The post is fixed to a door body in the rear portion in the longitudinal direction of the vehicle and extends in the height direction of the vehicle. The upper rim is fixed to the door body in the front portion in the longitudinal direction of the vehicle and connected to the upper end of the post. The post includes an outer member and an inner member each formed by press molding a plate made of a steel plate, for example. One edge portion of the outer member is curled such that one edge portion of the inner member is located in the curled edge portion. The other edge portion of the outer member and the other edge portion of the inner member are coupled with each other by welding. This integrates the members. For example, refer to Patent Document 1.
For example, as shown in FIGS. 8A and 8B, a folded portion 51, which is folded in the outward direction of the vehicle and further folded in the inward direction of the vehicle, is formed on the edge portion of the outer member 50 for welding. The folded portion 51 includes an opening 52, which opens in the inward direction of the vehicle. An extended portion 61, which extends in the outward direction of the vehicle, is formed on the edge portion of the inner member 60 for welding. The inner member 60 is temporarily coupled to the outer member 50 such that the edge portion of the extended portion 61 is inserted into the opening 52 of the folded portion 51. A basal portion 62, which extends in the outward direction of the vehicle, is provided on the distal end surface of the extended portion 61. A protrusion 63, which projects in the outward direction of the vehicle, is further provided on the central portion of the basal portion 62. The protrusion 63 contacts a facing portion 51a of the folded portion 51, which faces the protrusion 63 in the temporarily coupled state.
In the temporarily coupled state, the folded portion 51 of the outer member 50 and the extended portion 61 of the inner member 60 are tightly held and pressurized between two welding electrodes of a resistance welding device. When a welding electric current flows between the electrodes, as shown in FIGS. 8C and 8D, the protrusion 63 is melted by heating by the concentration of the electric current so that the basal portion 62 and the facing portion 51a are pressurized and joined with each other. As a result, the outer member 50 and the inner member 60 are coupled with each other to be integrated.